What’s the truth on mo­tor­way speeds?

FROM: Robert Brown MY daughter says there is zero tol­er­ance on mo­tor­way speeds, but an ad­vanced driv­ing in­struc­tor told me this is only true on smart mo­tor­ways, oth­er­wise there’s a lee­way of 10 per cent. A clear stan­dard would be help­ful to avoid con­fu­sion.